High-pressure injection systems of the common rail type encompass a pump that is embodied to pressurize liquid fuel in a specially furnished high-pressure collector (common rail) that feeds the injection apparatuses. The injection apparatus, which is referred to as a “common rail injector,” has an injection opening having a needle valve that can move in the injection body between a closed position and an open position. The position of the valve needle is determined by the intensity of two forces that are generated by the action of liquid under pressure on corresponding active surfaces and that act in opposite directions. The pressurized fuel in the chamber upstream from a sealing segment of the valve needle acts in the direction lifting the valve needle off its seat, and therefore in the opening direction. An electronically controlled control valve models the pressure in a control chamber, which acts on a surface in order to generate a force that, in the idle state, is greater than the first force and acts in a closing direction of the valve needle. Activation of the valve causes a decrease in the pressure level in the control chamber down to a point at which the force that is generated by the liquid fuel, and acts in order to permit opening, predominates over the first force and causes the valve needle to rise. This results in an injection of fuel.
In common rail injectors, component tolerances and wear cause injector- and runtime-dependent effects on injection behavior. These effects must be compensated for so that the injection behavior achieved is always the same. Different fuel properties, in particular fuel type and fuel temperature, furthermore also influence injector behavior. Good compensation for these effects requires an accurate knowledge of various injector properties.